1. Field of the Invention
The present invention relates to a rotating drum on whose peripheral surface a sheet material is wound such that the rotating drum supports the sheet material, and which can rotate in this state of supporting the sheet material. The present invention further relates to an image recording device using this rotating drum.
2. Description of the Related Art
Techniques (printing plate exposure devices) have been developed which, by using a sheet material, and in particular, a printing plate at which a photosensitive layer is provided on a support, record an image directly onto the photosensitive surface (emulsion surface) of the printing plate by a laser beam or the like. With such techniques, images can rapidly be recorded on printing plates.
In an automatic printing plate exposure device using a technique of recording an image on a printing plate, a printing plate is fed into an exposure section. The printing plate is thereby received at the exposure section, is positioned at a predetermined position, and is subjected to exposure processing.
Here, there is a method in which, in the exposure section, the printing plate is placed on a surface plate which supports the printing plate on a planar surface, and a recording head is moved relatively to the printing plate in the X-Y direction so as to carry out main scanning and subscanning to record an image. Further, there is a method in which the printing plate is trained on a rotating drum, and while the rotating drum is rotated at high speed (this is the main scanning), a recording head is moved along the axial direction of the rotating drum (this is the subscanning), so as to record an image on the printing plate.
In particular, in the method utilizing the rotating drum, high speed processing is possible because the rotating speed of the rotating drum is the speed of the main scanning. This method is also advantageous from the standpoint that the working space of the exposure section can be made to be more compact.
Because the rotating drum is rotated at high speed as described above, it is preferable that the rotating drum be formed of metal which has excellent durability. Further, while the rotating drum is rotating, the rigidity of the rotating drum must be ensured to the extent that it is difficult for the shaft to shake and the like.
Conventionally, the rotating drum is manufactured of an extruded material. However, in order to manufacture a large-diameter rotating drum without utilizing an extrusion molding device using a high pressure, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-033977 (which will hereinafter be referred to as the xe2x80x9cprior art documentxe2x80x9d) proposes a structure in which a rotating drum is divided by a plane passing through the substantial center of the circle of the rotating drum.
However, in the aforementioned prior art document, the plane of division is intended to be planar. It is easy for offset to arise between the adjacent divisional drums due to centrifugal force during rotation. Further, when the rotating drum rotates at high speed, a good image cannot be obtained at the regions of connection between the divisional drums.
Further, because the divisional drums are disposed so as to have line symmetry, there is much imbalance. A large deadweight is needed in order to achieve a balance, and the moment of inertia for rotation is large.
For these reasons, in the structure of the prior art document, it is extremely difficult to record an image by rotating a rotating drum at high speed.
Moreover, in the prior art document, fixing jigs are provided in the direction orthogonal to the axis of rotation, at the portions where the divisional drums are joined. Thus, assembling of the fixing jigs at the central portion in the axial direction of the drum cannot be carried out by using a regular tool, and complex work utilizing a special tool is required.
In view of the aforementioned, an object of the present invention is to provide a rotating drum and an image recording device in which, when the rotating drum is rotated at high speed, there is no offset between divisional drum parts, and there is little imbalance, and the moment of inertia for rotation is small.
Moreover, in addition to the above object, another object of the present invention is to provide a rotating drum which has a diameter which is larger than the maximum diameter of dies of an extrusion molding device used when the rotating drum is manufactured.
In order to achieve the above-described objects, in accordance with a first aspect of the present invention, there is provided a drum rotatable around a drum axis, and having a drum main body on whose outer peripheral surface a sheet is wound and held, the drum comprising: (a) a plurality of drum parts which are structured as if the drum main body is divided into plural parts in a peripheral direction, and which form the drum main body by being assembled together, and which can be separated from one another; and (b) joining elements which, at a time of assembling said drum, are positioned at borders of the drum parts which are adjacent, and which respectively extend parallel to the drum axis, and which are for joining the drum parts such that the drum parts can be separated from one another.
In accordance with another aspect of the present invention, there is provided an image recording device for forming an image on a printing plate, the image recording device comprising: (I) a drum rotatable around a drum axis, and having a drum main body on whose outer peripheral surface a printing plate is wound and held, the drum having: (a) a plurality of drum parts which are structured as if the drum main body is divided into plural parts in a peripheral direction, and which form the drum main body by being assembled together, and which can be separated from one another; and (b) joining elements which, at a time of assembling the drum, are positioned at borders of the drum parts which are adjacent, and which respectively extend parallel to the drum axis, and which are for joining the drum parts such that the drum parts can be separated from one another; and (II) a recording head portion disposed so as to oppose an outer peripheral surface of the drum, and having a recording head for recording an image on the printing plate.